# Question about the cyclic hemiacetal form of compounds [closed]

Why is D not a valid answer for this question?

• D is formed from 5-hydroxypentanal, a primary alcohol. Your compound is 4-hydroxypentanal. B is the answer. – user55119 Feb 4 '19 at 3:59
• Short and simple, if you count atoms from $\ce{O}$ (of $\ce{OH}$ group) to carbonyl $\ce{C}$, you'd find the number is 5. Thus, it makes 5-membered cycle. So, it can't be D. – Mathew Mahindaratne Feb 4 '19 at 4:17